U.S. patent application number 10/510334 was filed with the patent office on 2005-07-14 for positive-electrode active material for non-aqueous electrolyte secondary cell and process for preparing the same.
Invention is credited to Nitta, Katsuhisa, Oesten, Ruediger, Suzuki, Ryuta.
Application Number | 20050153206 10/510334 |
Document ID | / |
Family ID | 28786315 |
Filed Date | 2005-07-14 |
United States Patent
Application |
20050153206 |
Kind Code |
A1 |
Oesten, Ruediger ; et
al. |
July 14, 2005 |
Positive-electrode active material for non-aqueous electrolyte
secondary cell and process for preparing the same
Abstract
A positive-electrode active material for non-aqueous electrolyte
secondary cells which combine improved discharge property and
operational safety, and a process for preparing the same are
provided. The positive-electrode active material comprises a base
and one or more layers for coating the base, wherein at least one
of the layers is a coating layer comprising one or more metallic
components and one or more components selected from the group
consisting of sulfur, selenium, and tellurium.
Inventors: |
Oesten, Ruediger; (Alsbach,
DE) ; Suzuki, Ryuta; (Jwaki-shi, Fukushima-Pref,
JP) ; Nitta, Katsuhisa; (Iwaki-shi, JP) |
Correspondence
Address: |
MILLEN, WHITE, ZELANO & BRANIGAN, P.C.
2200 CLARENDON BLVD.
SUITE 1400
ARLINGTON
VA
22201
US
|
Family ID: |
28786315 |
Appl. No.: |
10/510334 |
Filed: |
October 5, 2004 |
PCT Filed: |
February 26, 2003 |
PCT NO: |
PCT/EP03/01939 |
Current U.S.
Class: |
429/232 ;
252/182.1; 427/126.1 |
Current CPC
Class: |
H01M 4/366 20130101;
H01M 10/052 20130101; H01M 10/0525 20130101; H01M 4/505 20130101;
H01M 4/485 20130101; H01M 4/525 20130101; Y02E 60/10 20130101 |
Class at
Publication: |
429/232 ;
252/182.1; 427/126.1 |
International
Class: |
H01M 004/62; B05D
005/12 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 5, 2002 |
JP |
2002-103764 |
Claims
1. A positive-electrode active material, comprising a base and one
or more layers for coating onto said base, wherein at least one of
said layers is a coating layer containing one or more kinds of
metallic components and one or more components selected from the
group consisting of sulfur, selenium, and tellurium.
2. The positive-electrode active material according to claim 1,
characterized in that the coating layer contains more than two
kinds of metallic components.
3. The positive-electrode active material according to claim 1,
characterized in that the metallic component contained in the
coating layer is one or more kinds of components selected from the
group consisting of lithium, magnesium, aluminum, silicon,
chromium, iron, zirconium, niobium, indium, tungsten, and
cerium.
4. The positive-electrode active material according to claim 1,
characterized in that the base contains manganese component.
5. The positive-electrode active material according to claim 1,
characterized in that the base has a spinel structure.
6. The positive-electrode active material according to claim 1,
characterized in that the coating layer contains sulfur
component.
7. A non-aqueous electrolyte secondary cell comprising the
positive-electrode active material according to claim 1.
8. A process for preparing a positive-electrode active material,
comprising: dispersing a base into water; using a raw material
containing: one or more metallic components; and one or more
components selected from the group consisting of sulfur, selenium,
and tellurium, as the coating raw material; adding said coating raw
material into said dispersion liquid under the control of pH to
form a coating layer by a precipitation method; and filtering said
dispersion liquid followed by drying the same after a coating layer
is formed.
9. The process for preparing a positive-electrode active material
according to claim 8, characterized in that a material containing
manganese component is used as the base.
10. The process for preparing a positive-electrode active material
according to claim 8, characterized in that a material having a
spinel structure is used as the base.
11. The process for preparing a positive-electrode active material
according to claim 8, characterized in that a material containing
one or more components selected from the group consisting of
lithium, magnesium, aluminum, silicon, chromium, iron, zirconium,
niobium, indium, tungsten, and cerium is used as the metallic
component.
12. The process for preparing a positive-electrode active material
according to claim 8, characterized in that a material containing
sulfur component is used as the coating raw material.
13. The process for preparing a positive-electrode active material
according to claim 8, characterized in that a raw material
containing one or more metallic components is added simultaneously
with or in advance to the addition of the raw material containing
one or more components selected from the group consisting of
sulfur, selenium, and tellurium.
Description
DETAILED DESCRIPTION OF THE INVENTION
[0001] 1. Technical Field of the Invention
[0002] The present invention relates to a positive-electrode active
material for a non-aqueous electrolyte secondary
cell.quadrature.which has good discharge characteristics and
improved cycle characteristics while maintaining operational
safety, and to a process of preparing the same.
[0003] 2. Prior Art
[0004] Non-aqueous electrolyte secondary cells typified by lithium
ion secondary cells are characterized by having larger
electromotive forces and lighter weights compared to nickel cadmium
secondary cells, nickel hydrogen secondary cells, and the like, and
have been widely used in notebook-type computers, video camcorders,
and others. Regarding the lithium ion batteries, there is a need
for higher capacity, enhanced safety, and lower production cost
and, in view of prospective application to electric vehicles, there
is a particularly strong demand for safety and cost.
[0005] In most currently available lithium ion secondary cells, a
material including cobalt is employed as the positive-electrode
active material. The secondary cells, which utilize a positive
electrode dominantly composed of cobalt, have excellent discharge
capacities; however, they have a safety problem in that a leakage
or an explosion may occur in a worst case when they are subjected
to strong stimulations such as high temperatures, high voltages,
over charges, disconnections, and nail pricking. They also have a
problem in the high cost of the raw material. As the most potential
candidate to solve these problems, manganese based
positive-electrode active materials have gained much attention and
lithium ion secondary cells utilizing such materials have been
already commercialized. However, though lithium ion secondary cells
utilizing manganese based positive-electrode active materials have
excellent safety characteristics, they have inferior cycle
characteristics compared to the cells utilizing cobalt base
positive-electrode active materials and therefore have not become
mainstream. Their cyclic degradation is more pronounced at high
temperatures.
[0006] A technique to improve cell properties by exploiting a
doping of a foreign element into the positive-electrode active
material is disclosed, for example, in JP-A-H03-219571; however, it
has not achieved satisfactory performances though it exhibited
improvement to some extent. There is disclosed another technique in
which a coating layer is applied on the surface of the
positive-electrode active material to improve cell properties. Such
technique is disclosed in, for example, JP-A-H09-171813,
JP-A-H08-236114, JP-A-H08-222219, JP-A-H08-102332, JP-A-H07-288127,
JP-A-H09-035715, JP-A-H 11-185758, JP-A-2001-313034, WO97-49136,
Electrochem. solid-state left. (1999) p 607, etc., but this
technique has not achieved a satisfactory performance either.
[0007] Problems to be Solved by the Invention
[0008] Accordingly, the object of the present invention is to
provide a positive-electrode active material for non-aqueous
electrolyte secondary cells which has improved discharge
characteristics and good cycle characteristics while maintaining
safety and a process for preparing the same.
[0009] Means for Solving the Problems
[0010] The inventors of the present invention have carried out
eager investigations to solve the above described problems and,
over the course of the investigation, they focused on the point
that part of the positive-electrode active material is supposed to
be dissolved into the electrolyte and precipitated at the negative
electrode thereby changing the electrical potential during
repeating charging/discharging cycles, and have found that the
stability of the positive-electrode active material is remarkably
improved by applying a coating layer containing specific components
on the positive-electrode active material thereby preventing the
dissolution of the positive-electrode active material and thus the
above described problems can be solved, and eventually completed
the invention.
[0011] Accordingly, the present invention relates to a
positive-electrode active material comprising a base and one or
more layers for coating said base, wherein at least one of said
layers is a coating layer containing one or more kinds of metallic
components and one or more components selected from the group
consisting of sulfur, selenium, and tellurium.
[0012] The present invention also relates to the above described
positive-electrode active material, characterized in that the
coating layer contains more than two kinds of metallic
components.
[0013] The present invention further relates to the above described
positive-electrode active material, characterized in that the
metallic component contained in the coating layer is one ore more
kinds of components selected from the group consisting of lithium,
magnesium, aluminum, silicon, chromium, iron, zirconium, niobium,
indium, tungsten, and cerium.
[0014] The present invention also relates to the above described
positive-electrode active material, characterized in that the base
contains manganese component.
[0015] The present invention further relates to the above described
positive-electrode active material, characterized in that the base
has a spinel structure.
[0016] The present invention also relates to the above described
positive-electrode active material, characterized in that the
coating layer contains sulfur component.
[0017] The present invention also relates to a non-aqueous
electrolyte secondary cell, which utilizes the above described
positive-electrode active material.
[0018] The present invention further relates to a process for
preparing a positive-electrode active material, comprising:
[0019] dispersing a base into water,
[0020] using a raw material containing one or more metallic
components and one or more components selected from the group
consisting of sulfur, selenium, and tellurium as the coating raw
material;
[0021] adding said coating raw material into said dispersion liquid
under the control of pH to form a coating layer by a precipitation
method; and
[0022] filtering said dispersion liquid followed by drying the same
after a coating layer is formed.
[0023] The present invention also relates to the above described
process for preparing a positive-electrode active material,
characterized in that a base containing manganese component is
used.
[0024] The present invention further relates to the above described
process for preparing a positive-electrode active material,
characterized in that a base having a spinel structure is used.
[0025] The present invention also relates to the above described
process for preparing a positive-electrode active material,
characterized in that a metallic component containing one or more
components selected from the group consisting of lithium,
magnesium, aluminum, silicon, chromium, iron, zirconium, niobium,
indium, tungsten, and cerium is used.
[0026] The present invention further relates to the above described
process for preparing a positive-electrode active material,
characterized in that a material containing sulfur component is
used as the coating raw material. The present invention also
relates to the above described process for preparing a
positive-electrode active material, characterized in that a raw
material containing one or more metallic components is added
simultaneously with or in advance to the addition of the raw
material containing one or more components selected from the group
consisting of sulfur, selenium, and tellurium.
[0027] The positive-electrode active material of the present
invention is applied with a coating layer containing metallic
components and specific components thereby improving its chemical
stability and cycle characteristics. Since the positive-electrode
active material of the present invention has a coating layer, there
is less chance of the contact between the high potential
positive-electrode active material and the electrolyte, and
therefore the batteries using this material shows high safety under
special situations such as overcharges and nail pricking. When a
manganese base material is used as the positive-electrode active
material, the degradation of cycle characteristics which was a
problem in the prior art is improved and a good cycle
characteristics is maintained even at high temperatures, and thus a
positive-electrode active material having a good cycle
characteristics as well as a high level of safety is obtained.
Moreover, the positive-electrode active material of the present
invention has an excellent suitability for manufacturing such as
filterability and therefore enables easy manufacture of the above
described positive-electrode active material which has an ensured
chemical stability.
EMBODIMENTS OF THE INVENTION
[0028] In the present invention, an active material means a
component which relates to charging/discharging operation as the
principal component generating electric potential in the elements
constituting the cell, and includes the active material and the
negative-electrode active material. In the present specification, a
positive-electrode active material means the whole
positive-electrode active material including the coating layer, and
a base means the base material for the positive-electrode active
material before coating. Moreover, in the present specification, a
positive electrode includes a positive-electrode active material,
and other than that, includes components such as conductive agents,
binders, and additives, which are necessary components to perform
charging/discharging.
[0029] Metallic components contained in the coating layer of the
present invention include alkali metals, alkaline-earth metals,
transition metals, semimetals such as Pb and In, and more
preferable metallic components are Li, Na, Mg, Al, Si, K, Ca, Ti,
V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, In, W, and Ce. Any
one of these components may be selected, and it is preferable to
include more than two components together. Particularly preferable
components are Li, Mg, Al, Si, Cr, Fe, Zr, Nb, In, W, Ce, and it is
still more preferable to include more than two kinds of these
components together.
[0030] The raw materials for introducing the metallic components
are usable of any materials containing the desired metallic
component, including metal alkoxides, fluorides, chlorides,
oxychlorides, bromides, iodides, oxides, sulfides, selenides,
tellurides, hydroxides, nitrates, sulfates, acetates, salts of
organic acids, metal complex, and others.
[0031] Excepting metallic components, the components contained in
the coating layer of the positive-electrode active material
according to the present invention include oxygen, sulfur,
selenium, tellurium, and particularly at least one or more
components among sulfur, selenium, and tellurium are contained.
Particularly, oxygen and sulfur are preferable.
[0032] The raw material for introducing components other than
metallic components may include sulfur, fluorides, chlorides,
bromides, iodides, oxides, sulfide, selenides, tellurides,
hydroxides, nitrates, dithionates, disulfites, sulfites,
pyrosulfates, sulfates, selenates, tellurates, acetates, and other
salts of organic acids. These raw materials may contain metallic
components and, in such cases, may be the same material as the raw
material for introducing metallic components. Preferable raw
materials include sulfide, selenates, tellurates, dithionates,
disulfites, sufites, pyrosulfates, sulfates, selenates, and
tellurates.
[0033] The positive-electrode active material of the present
invention may have a plurality of layers if it includes the above
described coating layer; preferably the utmost surface layer
consists of a coating layer containing the above described
components.
[0034] The process for forming the coating layer of the present
invention may include, for example, baking onto the surface of the
active material by heating, electrochemical precipitation on the
surface, surface deposition by PVD, CVD, etc., surface deposition
by mechanical energy such as strong mixing, and chemical
precipitation on the surface, out of which chemical precipitation
on the surface is preferable.
[0035] As the process of chemical precipitation on the surface, an
alkoxide process, a precipitation method, and the like may be used.
The alkoxide process may be performed by giving rise to a
hydrolysis by adding metal alkoxide raw material, water, and raw
material for other necessary components to a liquid formed of the
base dispersed in a dispersion medium such as alcohol.
[0036] Examples of the precipitation method are (1) a method of
adding the base into the liquid in which raw materials containing
metallic components and other necessary raw materials are dissolved
and if desired, adjusting the pH, and (2) a method of adding the
raw material containing the metallic components and raw material
containing other necessary components into a liquid formed of the
base dispersed in a dispersion medium such as water and if desired,
adjusting the pH.
[0037] It is preferable to perform the pH adjustment simultaneously
with the addition of the raw material containing metallic
components and other raw materials. It is also preferable to
control the pH to maintain a desired value. The desired value is
not necessarily a constant value, and it is to be optimally set
throughout the reaction process. The material for controlling the
pH may be an aqueous solution of hydrates, ammonia, acetic acid,
hydrochloric acid, etc. and the adding rate of these materials need
not be constant, and may be varied for pH control. An aqueous
solution of lithium hydroxide or ammonia is preferable as the raw
material for pH control. The methods of controlling pH include an
electrical control method based on a feedback from a pH probe, and
a chemical control method based on the addition of a high capacity
buffering component.
[0038] The range of the set pH value varies depending on the kind
of active material which constitutes the base, and the raw
materials to be added. When, for example,
Li.sub.1.05Ni.sub.0.42Mn.sub.0.53O.sub.2 is used for the base, a
preferable pH is 7.5 to 9.0 for the case in which the metal
containing raw material is iron trichloride, and likewise 7.2 to
8.5 for zinc nitrate, 1.5 to 6.0 for zirconium oxychloride.
Further, when LiMn.sub.2O.sub.4 is used as the base, a preferable
pH is 3.0 to 6.0 for the case in which the metal containing raw
material is indium chloride, and likewise 4.0 to 6.0 for the case
in aluminum chloride, and 8.0 to 12.0 for the case in sodium
aluminate.
[0039] The preferable amount of the coating layer in the present
invention is 0.1 to 10% by weight with respect to the
positive-electrode active material for the base, and more
preferably 0.2 to 5%, and still more preferably 0.8 to 3%. The
analysis of the components of the coating layer may be conducted in
various ways. Examples include an analysis using atomic absorption
spectroscopy or ICP by dissolving the specimen, and an analysis by
ESCA, SIMS, etc.
[0040] The reaction for the surface coating is preferably conducted
at a raised temperature; preferably not lower than 30.degree. C.
and not higher than 95.degree. C., and more preferably not lower
than 40.degree. C. and not higher than 80.degree. C. It is also
preferable that the reaction is performed with stirring.
[0041] It is preferable to perform filtering after the reaction for
the coating is completed. Since, in the coating specimen obtained
by the above described reaction, almost all the added coating raw
material is consumed for the coating, a good filterability is
achieved. Therefore, the above described reaction is preferable in
view of the suitability for manufacturing. The filtered coating
specimen may be heat treated as desired. The temperature of the
heat treatment is preferably not lower than 100.degree. C. and not
higher than 750.degree. C., and more preferably not lower than
200.degree. C. and not higher than 500.degree. C.
[0042] In the present invention, various positive-electrode active
materials may be used as the base for the coating. Depending on the
kind of the non-aqueous electrolyte secondary cell to be developed,
the base may be formed by using metal oxides, etc. For example, to
form a lithium ion non-aqueous electrolyte secondary cell,
materials containing metallic component such as Co, Ni, Mn, etc may
be used, and more specifically LiCoO.sub.2, LiNiO.sub.2,
Li.sub.vCo.sub.xNi.sub.yMn.sub.zO.sub.2 (0.4.ltoreq.v.ltoreq.1.05,
0.ltoreq.x.ltoreq.0.20, 0.ltoreq.y.ltoreq.0.50,
0.40.ltoreq.z.ltoreq.2.10) may be mentioned and LivCoxNiyMnzO.sub.2
(0.4.ltoreq.v.ltoreq.1.05, 0.ltoreq.x.ltoreq.0.20,
0.ltoreq.y.ltoreq.0.50, 0.40.ltoreq.z.ltoreq.2.10) is preferable.
In view of the safety, a material containing Mn is preferable and
also a material having a spinel structure is preferable.
[0043] The negative-electrode active materials which may be used in
the present invention include alkaline metals such as lithium,
alloys of alkaline metals, carbon materials, and oxides which can
occlude and release alkaline metals.
[0044] The non-aqueous electrolytic solution which may used in the
present invention includes, for example, propylene carbonate,
ethylene carbonate, diethyl carbonate, methyl ethyl carbonate,
1,2-dimethoxyethane, 1,2-diethoxyethane, .gamma.-butyrolactone,
tetrahydrofuran, 1,3-dioxolane, dipropyl carbonate, diethyl ether,
sulfolane, methyl sulfolane, acetonitrile, propyl nitrile, anisole,
acetic ester, ester of propionic acid, etc., and any combination of
more than two kinds selected from these also may be used.
[0045] As the electrolyte to be dissolved in the non-aqueous
electrolytic solution, salts of alkaline metals such as lithium and
sodium can be used and a proper material is to be selected
depending on the kind of the non-aqueous electrolytic solution
cell. In the case of, for example, a lithium ion secondary cell,
LiClO.sub.4, LiAsF.sub.6, LiPF.sub.6, LiBF.sub.4,
LiCF.sub.3SO.sub.3, LiN(CF.sub.3SO.sub.2).sub.2,
Li[(C.sub.2F.sub.5).sub.3PF.sub.3], etc. may be used, and any of
these may also be mixed.
[0046] Although there is no limitation on the shape of the
non-aqueous electrolyte secondary cell including the
positive-electrode active material of the present invention,
examples of the shape include, for example, cylindrical shape,
square-type, coin-type, button-type, paper-type, etc.
[0047] There is also no limitation on the uses of the non-aqueous
electrolyte secondary cell, and they may be used in notebook-type
computers, mobile phones, video camcorders, digital cameras,
portable MDs, portable game machines, portable CD players, back-up
power supplies, automobiles, large scale storage batteries, and the
like.
EXAMPLES
[0048] The present invention will be described in more detail
referring to examples, but these will not limit the invention.
Example 1
[0049] 500 g of water was added to 100 g of
Li.sub.1.03Mn.sub.2O.sub.4 having a spinel structure and being the
base of the positive electrode active material with stirring. The
temperature of the mixture was regulated at 60.degree. C. and a
liquid prepared by dissolving 4.66 g of cobalt chloride hexahydrate
and 0.40 g of sodium sulfite into 50 g of water was added thereto
while regulating the pH at 8.5 by properly adding 1% aqueous
solution of lithium hydroxide. Upon completion of the addition, the
mixture was stirred for one more hour and then filtered. The
filtered specimen was dispersed in 500 g of water and filtered
again and, after repeating this process twice, was dried. The
specimen was then heat treated at 450.degree. C. for 30 minutes to
obtain the specimen S1 for the example 1. The coating layer
contained cobalt, oxygen, and sulfur.
Example 2
[0050] 500 g of water was added to 100 g of
Li.sub.1.03Mn.sub.2O.sub.4 having a spinel structure and being the
base of the positive electrode active material with stirring. The
temperature of the mixture was regulated at 45.degree. C. and 1%
aqueous solution of acetic acid was added until the pH reached 5.4.
Thereafter, a liquid prepared by dissolving 4.73 g of aluminum
chloride hexahydrate and 0.56 g of lithium sulfate monohydrate into
50 g of water was added thereto while regulating the pH at 5.4 by
properly adding 1% aqueous solution of lithium hydroxide. Upon
completion of the addition, the mixture was further stirred for 10
hours and then filtered. The filtered specimen was dispersed in 500
g of water and filtered again and, after repeating this process
twice, was dried. The specimen was then heat treated at 290.degree.
C. for 30 minutes to obtain the specimen S2 for the example 2. The
coating layer contained aluminum, oxygen, and sulfur.
Example 3
[0051] 500 g of water was added to 100 g of
Li.sub.1.03Mn.sub.1.95CO.sub.0- .05O.sub.4 having a spinel
structure and being the base of the positive electrode active
material with stirring. The temperature of the mixture was
regulated at 75.degree. C. and a liquid prepared by dissolving 3.92
g of ferrous chloride tetrahydrate and 0.20 g of sodium sulfite
into 50 g of water was added thereto while regulating the pH at 8.3
by properly adding 1% ammonium aqueous solution. Upon completion of
the addition, the mixture was further stirred for one hour and then
filtered. The filtered specimen was dispersed in 500 g of water and
filtered again and, after repeating this process twice, was dried.
The specimen was then heat treated at 450.degree. C. for 20 minutes
to obtain the specimen S3 for the example 3. The coating layer
contained iron, oxygen, and sulfur.
Example 4
[0052] 500 g of water was added to 100 g of
Li.sub.1.03Mn.sub.1.95Co.sub.0- .05O.sub.4 having a spinel
structure and being the base of the positive electrode active
material with stirring. The temperature of the mixture was
regulated at 60.degree. C. and a liquid prepared by dissolving 2.67
g of zinc chloride and 0.20 g of sodium sulfite into 50 g of water
was added thereto while regulating the pH at 7.5 by properly adding
1% ammonium aqueous solution. Upon completion of the addition, the
mixture was further stirred for 3 hours and then filtered. The
filtered specimen was dispersed in 500 g of water and filtered
again and dried. The specimen was then heat treated at 480.degree.
C. for 20 minutes to obtain the specimen S4 for the example 4. The
coating layer contained zinc, oxygen, and sulfur.
Example 5
[0053] 500 g of water was added to 100 g of
Li.sub.1.03Mn.sub.2O.sub.4 having a spinel structure and being the
base of the positive electrode active material, and 1.10 g of
lithium acetic anhydride with stirring. The temperature of the
mixture was regulated at 60.degree. C. and a liquid prepared by
dissolving 4.66 g of cobalt chloride hexahydrate and 0.40 g of
sodium sulfite into 50 g of water was added thereto while
regulating the pH at 8.5 by properly adding 1% aqueous solution of
lithium hydroxide. Upon completion of the addition, the mixture was
stirred for one more hour and then filtered. The filtered specimen
was dispersed in 500 g of water and filtered again and, after
repeating this process twice, was dried. The specimen was then heat
treated at 450.degree. C. for 30 minutes to obtain the specimen S5
for the example 5. The coating layer contained cobalt, lithium,
oxygen, and sulfur.
Example 6
[0054] 500 g of water was added to 100 g of
Li.sub.1.03Mn.sub.2O.sub.4 having a spinel structure and being the
base of the positive electrode active material with stirring. The
temperature of the mixture was regulated at 45.degree. C. and a
liquid prepared by dissolving 1.10 g of lithium acetate into 50 g
of 1.5% aqueous solution of acetic acid was added thereto while
regulating the pH at 5.4 by properly adding 1% aqueous solution of
lithium hydroxide. Upon completion of the addition, the mixture was
further stirred for 10 hours and then filtered. The filtered
specimen was dispersed in 500 g of water and filtered again and,
after repeating this process twice, was dried. The specimen was
then heat treated at 290.degree. C. for 30 minutes to obtain the
specimen S6 for the example 6. The coating layer contained
aluminum, lithium, oxygen, and sulfur.
Example 7
[0055] 500 g of water was added to 100 g of
Li.sub.1.03Mn.sub.2O.sub.4 having a spinel structure and being the
base of the positive electrode active material with stirring. The
temperature of the mixture was regulated at 45.degree. C. and 1%
aqueous solution of acetic acid was added until the pH reached 5.3.
Thereafter, a liquid prepared by dissolving 4.26 g of aluminum
chloride hexahydrate, 0.58 g of indium choloride tetrahydrate, and
0.21 g of lithium sulfate monohydrate into 50 g of water was added
thereto while regulating the pH at 5.3 by properly adding 1%
aqueous solution of lithium hydroxide. Upon completion of the
addition, the mixture was further stirred for 0.10 hours and then
filtered. The filtered specimen was dispersed in 500 g of water and
filtered again and, after repeating this process twice, was dried.
The specimen was then heat treated at 290.degree. C. for 30 minutes
to obtain the specimen S7 for the example 7. The coating layer
contained aluminum, indium, oxygen, and sulfur.
Example 8
[0056] 500 g of water was added to 100 g of
Li.sub.1.03Mn.sub.2O.sub.4 having a spinel structure and being the
base of the positive electrode active material with stirring. The
temperature of the mixture was regulated at 45.degree. C. and 1%
aqueous solution of acetic acid was added until the pH reached 5.8.
Thereafter, a liquid prepared by dissolving 4.26 g of aluminum
chloride hexahydrate, 0.47 g of cobalt chloride hexahydrate, and
0.20 g of sodium sulfite into 50 g of water was added thereto while
regulating the pH at 5.8 by properly adding 1% aqueous solution of
lithium hydroxide. Upon completion of the addition, the mixture was
further added with the 1% aqueous solution of lithium hydroxide to
raise its pH to 8.5, and was stirred for 3 hours and then filtered.
The filtered specimen was dispersed in 500 g of water and filtered
again and, after repeating this process twice, was dried. The
specimen was then heat treated at 290.degree. C. for 30 minutes to
obtain the specimen S8 for the example 8. The coating layer
contained aluminum, cobalt, oxygen, and sulfur.
Example 9
[0057] The specimen S9 for the example 9 was prepared in an
analogous fashion with the example 8 except that
Li.sub.1.05Ni.sub.0.42Mn.sub.0.53O- .sub.2 was used as the base for
the positive electrode active material. The coating layer contained
aluminum, cobalt, oxygen, and sulfur.
Example 10
[0058] The specimen S10 for the example 10 was prepared in an
analogous fashion with the example 8 except that LiCoO.sub.2 was
used as the base for the positive electrode active material. The
coating layer contained aluminum, cobalt, oxygen, and sulfur.
Example 11
[0059] 500 g of water was added to 100 g of
Li.sub.1.03Mn.sub.2O.sub.4 having a spinel structure and being the
base of the positive electrode active material with stirring. The
temperature of the mixture was regulated at 45.degree. C. and 1%
aqueous solution of acetic acid was added thereto until its pH
reached 5.3.
[0060] Thereafter, a liquid prepared by dissolving 0.52 g of
chromium trichloride hexahydrate into 10 g of water was added
thereto while regulating the pH at 5.3 by properly adding 1%
aqueous solution of lithium hydroxide. The mixture was added with
the 1.% aqueous solution of lithium hydroxide until its pH reached
5.8, and thereafter a liquid prepared by dissolving 4.26 g of
aluminum chloride hexahydrate, 0.47 g of cobalt chloride
hexahydrate, and 0.20 g of sodium sulfite into 50 g of water was
added thereto while regulating the pH at 5.8 by properly adding 1%
aqueous solution of lithium hydroxide. Upon completion of the
addition, the mixture was further added with the 1% aqueous
solution of lithium hydroxide to raise its pH to 8.5, and was
stirred for 3 hours and then filtered. The filtered specimen was
dispersed in 500 g of water and filtered again and, after repeating
this process twice, was dried. The specimen was then heat treated
at 290.degree. C. for 30 minutes to obtain the specimen S11 for the
example 11. The coating layer contained aluminum, cobalt, chromium,
oxygen, and sulfur.
Example 12
[0061] 500 g of water was added to 100 g of
Li.sub.1.03Mn.sub.2O.sub.4 having a spinel structure and being the
base of the positive electrode active material, with stirring. The
temperature of the mixture was regulated at 45.degree. C. and 1%
aqueous solution of acetic acid was added until the pH reached 5.3.
Thereafter, a liquid prepared by dissolving 0.73 g of cerium
trichloride heptahydrate into 10 g of water was added thereto while
regulating the pH at 5.3 by properly adding 1% aqueous solution of
lithium hydroxide. The mixture was added with the 1% aqueous
solution of lithium hydroxide until its pH reached 5.8, and
thereafter a liquid prepared by dissolving 4.26 g of aluminum
chloride hexahydrate, 0.47 g of cobalt chloride hexahydrate, and
0.20 g of sodium sulfite into 50 g of water was added thereto while
regulating the pH at 5.8 by properly adding 1% aqueous solution of
lithium hydroxide. Upon completion of the addition, the mixture was
further added with the 1% aqueous solution of lithium hydroxide to
raise its pH to 8.5, and was stirred for 3 hours and then filtered.
The filtered specimen was dispersed in 500 g of water and filtered
again and, after repeating this process twice, was dried. The
specimen was then heat treated at 290.degree. C. for 30 minutes to
obtain the specimen S12 for the example 12. The coating layer
contained aluminum, cobalt, cerium, oxygen, and sulfur.
Example 13
[0062] 500 g of water was added to 100 g of
Li.sub.1.03Mn.sub.2O.sub.4 having a spinel structure and being the
base of the positive electrode active material, and 0.20 g of
sodium sulfite with stirring. The temperature of the mixture was
regulated at 45.degree. C. and 1% aqueous solution of acetic acid
was added until the pH reached 5.8. Thereafter, a liquid prepared
by dissolving 4.26 g of aluminum chloride hexahydrate, and 0.47 g
of cobalt chloride hexahydrate into 50 g of water was added thereto
while regulating the pH at 5.8 by properly adding 1% aqueous
solution of lithium hydroxide. Upon completion of the addition, the
mixture was further added with the 1% aqueous solution of lithium
hydroxide to raise its pH to 8.5, and was stirred for 3 hours and
then filtered. The filtered specimen was dispersed in 500 g of
water and filtered again and, after repeating this process twice,
was dried. The specimen was then heat treated at 290.degree. C. for
30 minutes to obtain the specimen S13 for the example 13. The
coating layer contained aluminum, cobalt, oxygen, and sulfur.
Comparative Example 1
[0063] The specimen R1 for the comparative example 1 was prepared
in an analogous fashion with the example 1 except that sodium
sulfite was not added. The coating layer contained cobalt and
oxygen.
Comparative Example 2
[0064] The specimen R2 for the comparative example 2 was prepared
in an analogous fashion with the example 2 except that lithium
sulfate monohydrate was not added. The coating layer contained
aluminum and oxygen.
Comparative Example 3
[0065] The specimen R3 for the comparative example 3 was prepared
in an analogous fashion with the example 3 except that sodium
sulfite was not added. The coating layer contained iron and
oxygen.
Comparative Example 4
[0066] The specimen R4 for the comparative example 4 was prepared
in an analogous fashion with the example 4 except that sodium
sulfite was not added. The coating layer contained zinc and
oxygen.
Comparative Example 5
[0067] The specimen R5 for the comparative example 5 was prepared
in an analogous fashion with the example 5 except that sodium
sulfite was not added. The coating layer contained cobalt, lithium,
and oxygen.
Comparative Example 6
[0068] The specimen R6 for the comparative example 6 was prepared
in an analogous fashion with the example 6 except that lithium
sulfate monohydrate was not added. The coating layer contained
aluminum, lithium, and oxygen.
Comparative Example 7
[0069] The specimen R7 for Comparative example 7 was prepared in an
analogous fashion with the example 8 except that sodium sulfite was
not added. The coating layer contained aluminum, cobalt, and
oxygen.
Comparative Example 8
[0070] The specimen R8 for the comparative example 8 was prepared
in an analogous fashion with the example 9 except that sodium
sulfite was not added. The coating layer contained aluminum,
cobalt, and oxygen.
Comparative Example 9
[0071] The specimen R9 for the comparative example 9 was prepared
in an analogous fashion with the example 10 except that sodium
sulfite was not added. The coating layer contained aluminum,
cobalt, and oxygen.
[0072] Chemical Stability Test
[0073] The stability test was conducted by investigating the amount
of dissolution of manganese or cobalt into acetic acid while the
coating specimen was immersed in a 1000 ppm aqueous solution of
acetic acid. The amount of dissolution of manganese into the
aqueous solution of acetic acid are measured for the specimens
other than S10 and R9 and the amount of dissolution of cobalt was
measured for the specimens S10, R9 by means of a component
absorption photometry. The chemical stability test was also
conducted on the base specimens having no coating, and the amount
of dissolution of each coated specimen was represented by a
relative quantity of dissolution of each specimen having coating to
the base specimen having no coating as the reference 100. In this
measure, smaller figures show higher stability.
[0074] Manufacturing Suitability Test
[0075] According to the process of the present invention, the
manufacturing suitability of the coating of the positive electrode
active material will be improved. One of these features is improved
filterability. The evaluation was conducted on the first filtering
step in the process of preparing each coating specimen and the
filtration speed was represented by 5 steps such that the fastest
filtration speed is 5, and the slowest is 1.
1 TABLE 1 Base Coating Fil- Positive layer Chemical tration
Specimen Electrode composition stability speed Present Inv. S1 1
Co, S, O 75 3 Present Inv. S2 1 Al, S, O 65 4 Present Inv. S3 2 Fe,
S, O 65 5 Present Inv. S4 2 Zn, S, O 70 5 Present Inv. S5 1 Li, Co,
S, O 75 3 Present Inv. S6 1 Li, Al, S, O 50 4 Present Inv. S7 1 Al,
In, S, O 45 5 Present Inv. S8 1 Al, Co, S, O 40 5 Present Inv. S9 3
Al, Co, S, O 70 5 Present Inv. S10 4 Al, Co, S, O 85 5 Present Inv.
S11 1 Al, Co, Cr, 30 5 S, O Present Inv. S12 1 Al, Co, Ce, 30 5 S,
O Present Inv. S13 1 Al, Co, S, O 60 5 Comp. R1 1 Co, O 95 1
Example Comp. R2 1 Al, O 90 1 Example Comp. R3 2 Fe, O 90 2 Example
Comp. R4 2 Zn, O 95 2 Example Comp. R5 1 Li, Co, O 95 1 Example
Comp. R6 1 Li, Al, O 90 1 Example Comp. R7 1 Al, Co, O 90 1 Example
Comp. R8 3 Al, Co, O 90 1 Example Comp. R9 4 Al, Co, O 95 1 Example
The base positive electrodes are: 1: Li.sub.1.03Mn.sub.2O.sub.- 4,
2: Li.sub.1.03Mn.sub.1.95Co.sub.0.05O.sub.4, 3:
Li.sub.1.05Ni.sub.0.42M- n.sub.0.53O.sub.2, 4: LiCoO.sub.2.
[0076] As shown in Table 1, the specimens according to the present
invention is good in the chemical stability and the filterability
compared to the comparative examples. Moreover, among the specimens
according to the present invention, the specimens S5 to S8 which
contained more than two kinds of metals in their coating layers
showed better chemical stability compared to the specimens S1 and
S2.
[0077] Also the comparison between the specimens S8 to S10 and the
specimens R7 to R9 showed that positive-electrode active materials,
other than lithium manganate having a spinel structure, used as the
base proved some effects of the present invention, but the extents
of improvement were rather small.
[0078] The specimens S11 and S12, on which multiple-layer coating
was applied, showed greater effects in the improvement of the
chemical stability compared to the specimen S8 having a single
layer coating.
[0079] The specimen S13 according to the present invention, in
which the raw material containing sulfur was added prior to the
addition of metal raw materials, showed reduced chemical stability
compared to the specimen S8 in the case of simultaneous addition of
both raw material containing sulfur and the metal raw
materials.
[0080] The specimens in which sulfur was replaced with selenium or
tellurium showed similar effects, but the degrees of the
improvement were smaller compared to the specimens including
sulfur.
[0081] Coin type Battery Test
[0082] 91 wt % of the specimen S1, 6 wt % of polyvinylidene
fluoride, and 3 wt % of acetylene black were mixed and dispersed in
N-methyl-pyrrolidone. Then the mixture was applied on a aluminum
foil of a 20 .mu.m thickness and dried, and the coated foil was
compressed by a roller press machine and thereafter stamped to form
a disc of a 13 mm diameter thus obtaining a positive-electrode
formed on the aluminum foil. This was placed in a
positive-electrode retainer. 85 wt % of graphite powder, 12 wt % of
polyvinylidene fluoride, and 3 wt % of acetylene black were mixed
and was dispersed in N-methyl-pyrrolidone. Then the mixture was
applied on a copper foil of a thickness of 20 .mu.m and dried, and
the coated foil was compressed by a roller press machine and
thereafter stamped to form a disc of 13 mm diameter thus obtaining
a negative-electrode formed on the copper foil. This electrode was
placed in a negative-electrode retainer. An electrolyte was formed
by dissolving a 1 mol/l concentration of LiPF.sub.6 into the liquid
formed by mixing propylene carbonate and diethyl carbonate by a
volume ratio of 1/1. This electrolyte was injected into the
positive-electrode retainer in which the specimen was placed, and a
separator made of polypropylene was placed thereon. Then the
positive-electrode retainer and negative-electrode retainer were
joined and sealed with a caulking machine to form a coin battery
CS1.
[0083] The coin batteries CS2 to CS13 were prepared by using the
specimens S2 to S13 instead of the specimen S1 used in the coin
battery CS1.
[0084] The coin batteries CR1 to CR9 were prepared by using the
specimens R1 to R9 instead of the specimen S1 used in the coin
battery CS1.
[0085] The coin batteries CB1 to CB4 were prepared by using the
base positive-electrodes 1 to 4 in place of the specimen S1 used in
the coin battery CS1.
[0086] These coin batteries were charged and discharged under
conditions of a temperature of 60.degree. C., a charge current of 2
mA, a terminal charge voltage of 4.2 V, a discharge current of 2
mA, and a terminal discharge voltage of 3.0 V. The ratio of the
discharge capacity after 50 cycles with respect to that of the
first cycle is evaluated as a holding ratio of capacity.
2 TABLE 2 Holding ratio of Capacity Coin (%) Battery 60.degree. C.
CS1 77 CS2 82 CS3 82 CS4 80 CS5 78 CS6 85 CS7 87 CS8 88 CS9 80 CS10
75 CS11 90 CS12 90 CS13 84 CR1 62 CR2 55 CR3 56 CR4 61 CR5 62 CR6
50 CR7 53 CR8 55 CR9 69 CB1 30 CB2 41 CB3 52 CB4 68
ADVANTAGES OF THE INVENTION
[0087] The positive-electrode active materials of the present
invention is good (superior) in chemical stability and
manufacturing suitability, and the non-aqueous electrolyte
secondary cells of the present invention is good (superior) in
cycle characteristics.
BRIEF DESCRIPTION OF DRAWING
[0088] FIG. 1 is a schematic view of a coin battery according to an
embodiment of the present invention.
DESCRIPTION OF SYMBOLS
[0089] 1 positive electrode
[0090] 2 negative electrode
[0091] 3 separator
[0092] 4 positive-electrode retainer
[0093] 5 negative-electrode retainer
[0094] 6 positive-electrode collector
[0095] 7 negative-electrode collector
[0096] 8 insulation seal
* * * * *